The invention relates to a magnetic head having a core of a soft-magnetic material with a comparatively low saturation magnetization, a gap between gap-bounding faces in the core, each of said gap-bounding faces being coated with a layer of soft-magnetic material having a higher saturation magnetization than the material of the core, transition zones which are poor magnetic conductors being present between the core and the layers of soft-magnetic material.
Such a magnetic head is known from Japanese published Patent application No. 55-58824 (A). The soft-magnetic material of the core of said magnetic head is ferrite. The use of ferrites, in particular mono-crystalline-Mn-Zn-ferrites, as a magnetic core material for magnetic heads is much preferred in particular in systems for magnetic recording and playback, for example audio and video tape recorders, but also in memories having magnetic discs. Ferrites have a high resistance to detrition, a comparatively high specific electrical resistivity and good magnetic properties, for example, a low coercive force, a large permeability and a good frequency characteristic.
The magnetic field which is generated at the area of the gap by a magnetic head so as to write information on a magnetic medium is restricted by the saturation magnetization of the material of the core of the magnetic head. Magnetic heads for the present-day video recorders generally have a core of Mn-Zn-ferrite. This type of material has a saturation magnetization of approximately 0.5 Tesla at room temperature. Said magnetization satisfies, up to temperatures slightly above room temperature, the requirements imposed by writing of information on conventional tapes, for example CrO.sub.2 tapes having a coervice force H.sub.c of approximately 56 kA/m.
However, in order to improve the quality of the video recording process there is a tendency to replace the conventional magnetic tapes by magnetic tapes having a higher coervice force, for example, tapes based on pure Fe which have an H.sub.c of approxiamtely 80-160 kA/m.
A magnetic head having a core of a soft-magnetic material with a comparatively low saturation magnetization cannot write such tapes very well, In fact, for writing tapes with a large coercive force the magnetic field of the magnetic head should also be large, which causes problems in that the magnetic field cannot be larger than the saturation magnetization of the material of the core. Saturation effects occur first at the edges of the gap.
In the magnetic head disclosed in the Japanese Patent application No. 55-58824 (A) saturation effects are controlled by providing on each of the gap bounding faces a layer of a material having a higher saturation magnetization than the material of the core. Since these saturation effects occure first at the edges of the gap with increasing magnetization of the core, this known magnetic head can be magnetized more strongly.
However, it is also stated in Japanese Patent application No. 55-58824 (A) that an artificial gap is formed between the core and the layer of material having a higher saturation magnetization than the material of the core. This artificial gap is formed as a result of the magnetically poorly conducting transition zone between the ferrite and the layer provided. As a result the magnetic head as it were has a main gap and two subsidiary gaps. It will be obvious that such a gap configuration adversely influences playback with a magnetic head. In particular the frequency characteristic of the magnetic head is adversely influenced. In this Japanese Patent application an attempt is made to mitigate this disadvantage slightly by giving the magnetically poorly conductive transition zone an irregular contour. Such a measure, which is technically difficult to perform since the main gap should be straight and the layers provided should be comparatively thin to avoid eddy currents and adhesion problems, provides insufficient effect.